NOVBMBEE 12, 1920] 



SCIENCE 



453 



tween proteins and other bodies rests. The 

 experiments mentioned thus far in this paper 

 do not yet allow us to decide whether the 

 ions are " adsorbed " or in chemical combina- 

 tion with the proteins. We will now show 

 that acids and bases combine with proteins 



40 



38 



36 

 "^ 34 

 ^32 



S 30 



% 28 

 o 

 B 26 



and an alkali. This can be proved in the 

 following way. We know that a weak dibasic 

 or tribasic acid gives off one hydrogen ion 

 more readily than both or all three; while in 

 a strong dibasic acid, like HjSO^, both hydro- 

 gen ions are held with a sufficiently small 



pH 20 22 Z4 26 2.8 3.0 3.2 34 3.6 38 40 42 44 4.6 4S 



Fig. 1. The ordinates represent the c.c. of 0.1 N acid in 100 c.e. of 1 per cent, solution of isoelec- 

 tric gelatin required to Ibring the solution to the pH indicated in the abscissae. The curves for 0.1 

 N HjSO, and 0.1 N HNO3 are identical while the values for HsPOi and oxalic acid differ, being ap- 

 proximately in the ratio of HNO3: oxalic acid: HjPOj as 1: 2: 3. 



in the same way as they combine with 

 crystalline compounds, namely by the purely 

 chemical forces of primary valency. The 

 combination between acids and proteins is 

 analogous to that between acids and NH3, 

 and the combination between bases and pro- 

 teins is analogous to that between CH3COOH 



electrostatic force to be easily removed. If 

 the forces which determine the reaction be- 

 tween these acids and proteins are purely 

 chemical it would ■'ollow that three times as 

 many c.c. of 0.1 ]SrH3P0^ are required to bring 

 100 c.c. of 1 per cent, solution of isoelectric 

 tin to a given pH, e. g., 3.0, as are re- 



